U.S. Pat. No. 4,564,348 to Larsen, assigned to the assignee of the present invention, discloses plastic molds for manufacturing a plurality of soft contact lenses in a continuous or semicontinuous method of operation. A mold assembly having a plurality of mold units is filled with a polymerization mixture in a first dosing step, and the mold units are then covered with a convex mold member or lid as shown in FIG. 5, and the lids are brought to rest on the concave mold members properly aligned and without distortion. The lids are free to float and align themselves on the pool of polymerizable mixture held in the concave mold.
U.S. Pat. No. 4,640,489, also to Larsen, now assigned to the assignee of the present application, discloses a mold for making contact lenses wherein one of the two mold sections is relatively more flexible than the other. In addition, a number of mold constructions known to the prior art are discussed in the background portion of the specification of this patent.
U.S. Pat. No. 4,495,313, also to Larsen, and now assigned to the assignee of the present application, discloses a mold assembly in which shrinkage of the monomer mixture during polymerization creates a negative pressure which aligns the upper mold half and draws excess monomer into the cavity.
In the commercial application of the invention described in U.S. Pat. No. 4,640,489 it has been found advantageous to weight the upper male portion of the mold cavity with a fixed weight subsequent to assembly to seat the upper male mold half and to displace any excess monomer in the mold cavity into a space between the flanges, as illustrated in FIG. 1 of that patent, to form a HEMA ring which is preferentially adhered to the upper or male portion of the mold cavity by a corona discharge treatment of a portion of the male mold.
U.S. Pat. No. 5,658,602 discloses a method and apparatus for contact lens mold filling and assembly in which dosing and the assembly of the mold parts in the method takes place in a vacuum environment. Although the use of the vacuum allowed for faster assembly of the mold parts, the vacuum complicated the apparatus and the process and often required service to keep the apparatus and process functioning as intended. However, efforts to assemble the mold parts without a vacuum lead to increased numbers of defects in the contact lenses produced. The majority of defects appeared to be bubbles of air trapped in the reaction mixture.
There is a need for a method and apparatus for assembly of contact lens molds that will eliminate the need for a vacuum environment, yet provide contact lenses without defects.